This invention relates to the docking of an offshore structure with a submerged fixture and, more particularly, to the docking of a jacket with a submerged wellhead in establishing an offshore facility for the recovery of crude oil or gas.
The production of crude oil or gas from submerged formations is being carried out on an ever increasing scale. Various techniques for underwater recovery of crude products are disclosed for example in the following U.S. Pat. No. 3,572,044 issued to Pogonowski on Mar. 23, 1971; No. 3,618,661 issued to Peterman on Nov. 9, 1971; No. 3,628,604 issued to Childers et al on Dec. 21, 1971; No. 3,717,002 issued to O'Brien et al on Feb. 20, 1973; No. 3,744,561 issued to Shatto, Jr. et al issued on July 10, 1973; No. 3,913,669 issued to Brun et al on Oct. 21, 1975; and No. 3,943,725 issued to Pennock on Mar. 16, 1976. Offshore activities of this sort typically involve the installation of production tubing into the formation and connecting a wellhead fixture to the tubing at the sea floor. A riser is secured to the wellhead to conduct crude product from the formation to a drilling platform supported above the wellhead. Oftentimes, the platform is installed after installation of the wellhead by lowering a support jacket onto the water bed around the wellhead and mounting a platform thereon above the water surface. The riser is then connected between the wellhead and the platform.
Installation of the jacket around the wellhead poses certain technical problems since it is usually desirable to locate the wellhead in a particular alignment relative to the jacket to optimize the performance of subsequent activities, such as connection of the riser to the wellhead. As to the latter, it should be noted that in some instances the riser is pre-installed on the jacket by temporary welds before the jacket is transported to the worksite. Once the jacket has been upended and immersed around the wellhead, the temporary welds are broken and the riser is allowed to descend onto the wellhead. Therefore, a relatively high degree of alignment is desirable to carry out this procedure.
In the aforementioned Pogonowski patent, a jacket is provided with one or more annular guide collars. By passing these collars downwardly around the wellhead as the jacket is lowered, at least a general alignment of sorts will likely be established. However, in order to make docking of the jacket with the wellhead possible, the guide collars must be formed somewhat larger than the wellhead. This gives rise to the possibility that precision alignment will not be established between the wellhead and jacket. Moreover, in the event that the guide collar is not perfectly centered relative to the wellhead once the jacket begins to sink into the water bed, it is possible for the jacket to impose sideward forces on the wellhead tending to dislodge it from its anchoring.
It is, therefore, an object of the present invention to minimize or obviate problems of the sort discussed above.
It is another object of the invention to provide novel methods and apparatus for aligning an offshore structure relative to a submerged fixture.
It is a further object of the invention to provide novel methods and apparatus for aligning a jacket with a wellhead.
It is an additional object of the invention to provide novel methods and apparatus for aligning a conduit carried by a jacket with a wellhead to facilitate hookup of the conduit to the wellhead.
It is still another object of the present invention to enable a jacket to be aligned with a wellhead in a manner requiring no estimating or guesswork on the part of an operator.
It is one more object of the invention to provide novel means for docking a jacket with a wellhead while imposing minimum lateral stresses on the wellhead.
It is a further object of the invention to provide novel methods and apparatus for aligning a jacket with a wellhead involving a plurality of displaceable pins carried by the jacket and which are engageable with the wellhead to establish predetermined alignment of the jacket with the wellhead.